Method an device for introducing oxygen into water or aqueous solutions

ABSTRACT

In a process for transferring oxygen or an oxygen-containing gas into water or aqueous solutions in the treatment of water or aqueous solutions, oxygen or an oxygen-containing gas is added to the water or aqueous solution continuously or at intervals through an injector and simultaneously through at least one tube sparger.

The invention relates to a process and a device for transferring oxygeninto water or aqueous solutions in accordance with the preamble of claim1.

In many areas of the treatment of water or aqueous solutions, it isnecessary or advantageous to additionally introduce oxygen into theaqueous system. Processes for treating water or aqueous solutions are,for example, processes in wastewater treatment, wastewater purification,drinking water treatment, in the protection of water bodies or in fishfarming. For an economical oxidation procedure, the oxygen transfer,that is the ratio of the amount of oxygen dissolved to the amount ofoxygen supplied, must be as high as possible, but the energy expended ondissolving the oxygen must at the same time be as low as possible.

Thus, in wastewater purification processes in sewage treatment plantsusing the so-called activated sludge process, in which the various waterconstituents are oxidatively broken down or in part used to synthesizenew biomass in a first process stage, the so-called activation stage, bymicroorganisms (bacteria) suspended in the wastewater in an activationtank, the aqueous solution (wastewater) is aerated and sometimes oxygenis additionally supplied. The air or oxygen is introduced by aerationequipment such as candle aerators or disk aerators. Sewage treatmentplants and processes of this type are described, for example, in“Abwassertechnik” [wastewater engineering], Hosang and Bischof, 9thedition, Verlag B. G. Teubner, 1989. Tightening of the legalrequirements of wastewater purification and, possibly, increase in thedirt loading of the wastewater, frequently necessitates expansion andimprovement of existing sewage treatment plants, which leads toadditional oxygen transfer often being required. This can be achieved byconventional aeration equipment, for example candle aerators or diskaerators, an oxygenator or by tube spargers or injectors. The term“oxygenator” is taken to mean here a pressure vessel through which waterflows; the term “tube sparger” is used here for a perforated tube; theterm “injector” denotes a device which fundamentally consists of a pump,a Venturi tube and a mixing section, which is equipped, for example,with mixing nozzles and mixing tubes.

The object underlying the invention is to improve the process mentionedat the outset in such a manner that the oxygen transfer is maximized andat the same time the additional energy expenditure is relatively low.

This object is achieved by adding oxygen or an oxygen-containing gas tothe water or aqueous solution continuously or at intervals through aninjector and simultaneously at least one tube sparger. Surprisingly, ithas been found that the technical advantage achieved by this combinationis greater than the alternative use of the individual devices (injectoror tube sparger). This synergistic effect is surprising, since theoverall efficiency is markedly above that of the partial systems. Theadditional energy requirement in this case is minimal and theeconomically expedient control range between maximum and minimum oxygenfeed is relatively large. The optimum oxygen content and the optimumrate of oxygen to be fed are dependent on the water or aqueous solutionto be treated and the specific mode of operation of the plant in whichthe claimed process is used, and can be determined for the respectiveboundary conditions by a few simple experiments. A further advantage isthat the tube spargers and injectors give rise to only relatively lowcapital costs.

The oxygen-containing gas used is preferably pure oxygen. The term “pureoxygen” means here oxygen which has a minimum purity of approximately80% by volume. For example, technical-grade oxygen which is produced byliquefying air and typically complies with the purity specification“oxygen 2.01” (minimum purity 99% by volume) or “oxygen 2.5” (minimumpurity 99.5% by volume) can be used. Use of such technical-grade purityoxygen gases is possible if this permits an economic procedure to beachieved.

According to the invention, the ratio of the volumetric flow rates ofthe oxygen or oxygen-containing gas added via the injector to the oxygenor oxygen-containing gas added via the tube sparger is 10:1 to 1:10.

It is provided according to the invention that the volumetric flow rateof the oxygen or oxygen-containing gas added via the injector is 0.01 to0.5 m³ (S.T.P.)/h per m³ of water or aqueous solution and/or that thevolumetric flow rate of the oxygen or oxygen-containing gas added viathe tube sparger is 0.01 to 0.4 m³ (S.T.P.)/h per m³ of water or aqueoussolution.

According to the invention, the oxygen-containing gas or oxygen is fedto the wastewater in the activation stage in a biological wastewaterpurification plant. Preferably, the injector and the tube sparger arethen arranged in the aerobic region at the bottom of the activation tankof the biological wastewater purification plant.

According to the invention, the water enriched with oxygen in theinjector flows via one or more mixing nozzles into the tank containingthe water lower in oxygen and/or the oxygen-enriched water is mixed withthe tank water lower in oxygen via one or more mixing tubes.

The oxygen-containing gas or pure oxygen can be fed via all conventionalsupply methods, for example liquid storage tank, on-site processes or apipe from a network. The term “on-site processes” here means processesin which oxygen is produced from the ambient air directly on the site ofoxygen consumption. Supply via a pipe from a network is preferred, sinceit makes possible relatively high operating safety and high security ofsupply for a relatively low expenditure on equipment and small spacerequirement. The oxygen supply can advantageously be connected to thedevice for transferring the oxygen to the water or aqueous solution byan elastomer tube, in order to simplify assembly.

For certain applications it is advantageous that the oxygen-containinggas or pure oxygen replaces the conventional aeration only at intervals,but preferably for 5 to 50 minutes per hour. Preferably, theoxygen-containing gas or oxygen replaces the conventional aeration of abiological wastewater purification plant in the case of an increasedhydraulic loading, which can occur, for example, as the result of arainfall event.

It is likewise provided according to the invention that theoxygen-containing gas or oxygen is fed to the wastewater in addition tothe conventional aeration in the event of a higher pollutant loading ofthe wastewater or in the event of an increased energy requirement of thebiological wastewater purification plant.

The object underlying the invention is further achieved by a device inwhich the oxygen or an oxygen-containing gas is fed through an injectorand simultaneously through at least one tube sparger, two conicalfunnels having a perforated and/or slotted middle piece and a sleevearranged on the middle piece for gas feed being assigned to the Venturitube of the injector. The sleeve advantageously has a socket or a flangefor connecting a tube or pipe for feeding the oxygen.

It is further provided according to the invention to use, instead of thedescribed Venturi tube, a liquid jet gas compressor which can take inthe gas at atmospheric pressure or slight superatmospheric pressure, forexample at a superatmospheric pressure up to 100 mbar. The term “liquidjet gas compressor” is taken to mean here jet pumps for transporting andcompressing gases with simultaneous intense mixing with the propellantfluid. They consist of a head piece, exchangeable propellant nozzle withswirl body and diffuser.

The tube sparger preferably consists of a perforated elastomer tube inwhich the orifices for the outflow of the oxygen-containing gas oroxygen are not formed until an overpressure in the tube interior ofapproximately 0.2 to 0.5 bar is reached. This has the advantage that theorifices cannot become blocked even when no oxygen-containing gas oroxygen is flowing out from the orifices.

According to the invention, downstream of the injector is arranged apipe on which are arranged one or more mixing nozzles and/or one or moremixing tubes. Upstream of this pipe, advantageously, can be provided afurther pipe as absorption section for increasing the oxygen transfer.

According to the invention it is provided that additional internals orchanges in cross-section of the pipe inner diameter are arranged in thepipe downstream of the injector to increase the turbulence in the flowprofile. This causes an improved dispersion or very fine distribution ofthe gas bubbles. According to the invention, a static mixer can furtheralso be arranged in the pipe downstream of the injector to increase theturbulence in the flow profile. The mixer has three-dimensionalinternals to modify the flow in such a manner that oxygen bubbles aremore intensively subdivided.

EXAMPLES

In a test tank containing pure water and at a water depth of 2 m, toachieve the same amount of dissolved oxygen, 244 kg/h of oxygen neededto be transferred with sole use of tube spargers, and 222 kg/h of oxygenneeded to be transferred with sole use of an injector, whereas in thecase of the combined use of tube spargers and injector, the amount ofoxygen needed to be transferred was only 200 kg/h.

In experiments in sewage treatment plants, for example in a sewagetreatment plant for 12,000 population equivalents having a water depthof 2.5 m, the advantages of the inventive combination were still moreclearly evident. Thus, for the same amount of dissolved oxygen, 304 kg/hof oxygen were required with sole use of tube spargers, and 162 kg/h ofoxygen were required with sole use of an injector, but the same amountof dissolved oxygen was achieved by a transfer of only 108 kg/h ofoxygen with combined use of tube spargers and injector.

What is claimed is:
 1. A process for transferring an oxygen-containing gas into water or aqueous solutions in waste water treatment, which comprises adding the oxygen-containing gas to the water or aqueous solutions continuously or in intervals through an injector and simultaneously through at least one tube sparger, characterized in that pure oxygen is used as the oxygen-containing gas, and that a tube sparger is used which consists of a perforated elastomer tube, in which orifices for the outflow of the pure oxygen are not formed until an overpressure in the tube interior of at approximately 0.2 to 0.5 bar is reached.
 2. The process as claimed in claim 1, wherein the oxygen-containing gas used is pure oxygen.
 3. The process as claimed in claim 1, wherein the ratio of the volumetric flow rates of the oxygen or oxygen-containing gas added via the injector to the oxygen or oxygen-containing gas added via the tube sparger is 1:10 to 10:1.
 4. The process as claimed in claim 1, wherein the volumetric flow rate of the oxygen or oxygen-containing gas added via the injector is 0.01 to 0.5 m³ (S.T.P.)/h per m³ of water or aqueous solution.
 5. The process as claimed in claim 1, wherein the volumetric flow rate of the oxygen or oxygen-containing gas added via the tube sparger is 0.01 to 0.4 m³ (S.T.P.)/h per m³ of water or aqueous solution.
 6. The process as claimed in claim 1, wherein the oxygen-containing gas or oxygen is fed to the wastewater in the activation stage in a biological wastewater purification plant.
 7. The process as claimed in claim 6, wherein the water enriched with oxygen in the injector flows via one or more mixing nozzles into the tank containing the water lower in oxygen.
 8. The process as claimed in claim 6, wherein the oxygen-enriched water is mixed with the tank water lower in oxygen via one or more mixing tubes.
 9. The process as claimed in claim 6, wherein the oxygen-containing gas or oxygen is fed to the water or aqueous solution via a pipe from a network.
 10. The process as claimed in claim 9, wherein the oxygen-containing gas of oxygen is fed to the wastewater in addition to the conventional aeration in the event of a higher pollutant loading of the wastewater or in the event of an increased energy requirement of the biological wastewater purification plant.
 11. The process as claimed in claim 9, wherein the oxygen-containing gas or oxygen replaces the conventional aeration in the event of an increase in hydraulic loading of the biological wastewater purification plant.
 12. The process as claimed in claim 6, wherein the oxygen-containing gas or oxygen replaces the conventional aeration for a period of 5 to 50 minutes per hour.
 13. The process as claimed in claim 1, wherein the oxygen or oxygen-containing gas is added to the water or aqueous solution continuously.
 14. The process as claimed in claim 1, wherein the oxygen or oxygen-containing gas is added to the water or aqueous solution at intervals.
 15. The process as claimed in claim 1, wherein the oxygen-containing gas is added in intervals. 